The present invention relates to a dispensing system and method in which an aqueous solution is dispensed from pressure vessels charged with a pressurized gas to drive the aqueous solution to one or more points of use. More particularly, the present invention relates to such a system and method in which the pressurized gas is humidified to at least inhibit the pressurized gas from taking up moisture from the aqueous solution.
Liquids made up of aqueous solutions of chemicals are dispensed from a variety of different devices that incorporate pressure vessels to drive the liquid to an end point of use. The pressure vessel is charged with a pressurized gas such as nitrogen to provide the motive force to drive the chemical to the intended point of use. An example of such device can be found in U.S. Pat. No. 5,148,945. In this patent, multiple pressure vessels are used to produce a continuity in the delivery of the liquid being dispensed. Other systems utilize only a single pressure vessel to accomplish the dispensing.
Generally, dry, ultra-high purity nitrogen is used to charge the pressure vessels to prevent contamination of the liquid chemical to be dispensed. However, dry nitrogen will over time pick up moisture from the liquid and change the character of the solution. Thus, when slurries are being dispensed, such take up of moisture produces unwanted drying and caking of the slurry within the pressure vessels. This caking is to be avoided, especially where the end use is a semiconductor polishing or planarization tool because the particles created can cause wafer defects.